Blow Molding Process

Blow molding is an umbrella term for forming hollow plastic parts by inflating a viscous plastic tube, or parison, until it fills a mold and forms the desired shape. Think of it like inflating a balloon inside of a water bottle.

There are three main types of blow molding: injection blow molding, stretch blow molding, and extrusion blow molding. Injection and stretch blow molding are often used to create water bottles, cosmetic containers, and other small hollow parts. Extrusion blow molding is used to create medium to large hollow parts with complex geometries or highly technical requirements such as DEF tanks, HVAC ducts, and lawn mower seats.

Extrusion Blow Molding Process

The first step in the extrusion blow molding manufacturing process is the extrusion of a tube, also called a “parison”, of viscous plastic into a product mold. The mold closes around the parison and air is pumped in to inflate the parison against the mold walls. Once the plastic cools back to a solid state, the mold opens and the part is ejected. Finally, the excess material along the mold pinch line is removed by a process called deflashing and the part is ready to undergo any secondary operations that are needed to finish the part.

Compression molding and insert molding are often combined with the process of extrusion blow molding in order to maintain ID and OD tolerances and add features to the product:

Plastic Compression Molding

Typically, extrusion blow molding plastic is suited for tight control of the outer diameter (OD) of a part but does not allow for completely accurate tolerances of the interior diameter (ID). By combining the plastic compression molding process with the blow molding process, we can precisely control both the OD and ID of your part.

Plastic Insert Molding

In the case of integrating plastic insert molding with the process of blow molding plastic, we can incorporate fasteners and/or other inserts directly within the mold. This eliminates steps in the production process such as riveting or welding which add time without adding value, and creates a stronger bond between the blow-molded and insert-molded components.

Is Blow Molding Right For Me?

Blow molding is the fastest and most cost-effective plastic molding process when production volume reaches 3,000+ parts per year. With an increasing focus on lightweighting and sustainability, it’s no wonder why engineers across the globe in nearly every industry have turned an eye towards blow molding for their high-production needs. Among its many benefits include:

Low cost for high volume production – Blow molding is more cost-efficient than other processes such as rotomolding and thermoforming for mass-produced hollow parts.

High strength-to-weight ratio – Parts can be reinforced with a lightweight foam core or internal ribs to increase structural strength and impact resistance.

Design flexibility – Complex part geometries can be achieved to adapt to unusual spaces between already existing components.

Insulation and acoustical properties – Hollows can be vacuumed or filled with a material to achieve high insulation and noise reduction properties

Getting Started

If you’re new to blow molding and don’t know where to start, then our free Blow Mold Design Guide is for you! It will provide you with basic design guidelines for the injection, stretch, and extrusion blow molding methods so you can determine if this process is right for you.

Sourcing a Supplier

Regency Plastics has over 30 years of technical blow molding experience. We know the importance of seeing each project through from inception to final production. First and foremost, Regency’s express intent with each new opportunity is to determine if there is a good fit for our blow molding process. If there is, we will assist you on material, process, pricing, logistics, quality, and DFM/DFA issues. On the other hand, if there isn’t a good fit we will do our best to connect you with someone who is better suited to fill the needs of your specific project.